CVE-2026-82260

Executive Summary

CVE-2026-82260 is a memory exhaustion vulnerability affecting SvelteKit (@sveltejs/kit) versions 2.49.0 through 2.52.1, specifically when the experimental.remoteFunctions option is enabled alongside form handling. An unauthenticated remote attacker can send crafted malformed form data to a vulnerable server, causing excessive memory allocation that crashes the server process — a denial of service (DoS) condition. The vulnerability is rated CVSS 7.5 (High) with network attack vector, low attack complexity, and no privileges or user interaction required. The fix is available in version 2.52.2; however, at the time of this writing, no formal patch advisory, workaround documentation, or exploit code has been publicly released, and the SvelteKit team has not yet confirmed patch availability from independent sources.

Affected parties are production web applications built with SvelteKit that run on the vulnerable versions and have explicitly enabled the experimental remote functions feature in their configuration — this is not a default configuration. The business impact is primarily availability-focused: a successful attack results in complete server process crash, leading to service downtime. No data confidentiality or integrity is compromised per the CVSS vector (C:N/I:N), but the high availability impact (A:H) combined with the unauthenticated, low-complexity exploitation makes this a serious operational risk for affected deployments.

Technical Analysis

The vulnerability resides in the deserialization routine used by SvelteKit's remote form functionality. SvelteKit's experimental remote functions feature allows client-side forms to invoke server-side functions (remote procedure calls) over HTTP, bypassing traditional API route definitions. When this feature is enabled in svelte.config.js under experimental.remoteFunctions, the framework serializes and deserializes form data at the server boundary to map incoming request bodies to typed function arguments.

The root cause is an unbounded memory allocation path during the parsing of the incoming form payload. The NVD description states that "malformed form data can cause excessive memory allocation." This indicates a lack of input size validation or a weakness in the parser's handling of deeply nested or recursively structured form fields. In multipart/form-data or URL-encoded form parsing, an attacker can craft nested key-value pairs or extremely long field names/values that cause the deserializer to allocate memory proportional to the depth or size of the structure, rather than being bounded by the actual HTTP body size or a configured limit.

The attack surface is the HTTP endpoint that accepts form submissions when the remote functions feature is in use. Because SvelteKit's remote functions are implemented via a single catch-all route that dispatches based on function name (an implementation detail not confirmed in the CVE description), any attacker who can reach the web server can submit a crafted POST request. The vulnerability class is CWE-400 — Uncontrolled Resource Consumption — specifically a "resource exhaustion" subtype where an excessive allocation leads to out-of-memory conditions in the Node.js runtime. When Node.js runs out of heap memory, it terminates the process, and the SvelteKit server (typically running under PM2, systemd, or a container orchestrator) either crashes entirely or enters a crash-restart loop. In single-instance deployments without process supervision, the service remains down until manual intervention.

Code-level details are limited. The NVD description does not specify the exact parsing function, the structure of the malformed data, or the allocation trigger point. This is consistent with the SvelteKit team's typical security practice of withholding exploit details until a broad install base has patched. What is known: the vulnerable code path is exclusively within the remote function deserializer, activated only when experimental.remoteFunctions is true. Applications using standard SvelteKit form actions (use:enhance, +page.server.js form handlers) are not affected unless they also enable remote functions.

Exploitation Scenarios

No public PoC or exploit code is currently available; the attack chain below is inferred from the vulnerability class (uncontrolled memory allocation in a network-facing deserializer).

Step 1 — Reconnaissance / Target Identification: An attacker first identifies SvelteKit-based applications. This is achieved through HTTP response headers (e.g., x-powered-by: SvelteKit), distinctive HTML source markers (e.g., SvelteKit's generated __sveltekit script tags), or by querying known form endpoints. The attacker then probes whether the experimental.remoteFunctions feature is enabled. This may be observable via an HTTP OPTIONS response listing non-standard form handlers, or by sending a benign POST to a known form action and observing a different response pattern than a standard form action (e.g., 405 Method Not Allowed versus a typed error). Alternatively, an attacker may fingerprint the application version via its bundle hash and match it against known vulnerable SvelteKit releases (2.49.0 through 2.52.1).

Step 2 — Flaw Class Trigger: The attacker crafts a malformed form submission targeted at the remote function deserializer. Since the exact payload structure is undisclosed, an attacker would rely on fuzzing: sending multipart/form-data bodies with deeply nested boundary headers, extremely long field names, or MIME parts with dangling boundaries. The goal is to trigger the parser's excessive allocation path. Because the vulnerability is in deserialization, the attacker must send a payload that the server attempts to parse — meaning the request must pass initial routing and be delivered to the remote function handler. The attacker does not need valid credentials, as the vulnerability is in the parsing layer, before any application-level authorization checks.

Step 3 — Payload / Execution Method (vulnerability-class level): The payload is a crafted HTTP POST request with content type application/x-www-form-urlencoded or multipart/form-data. Malformed form data — such as a single field name of hundreds of megabytes, thousands of nested [] array indices, or a multipart body with inconsistent Content-Length headers — causes the deserializer to allocate memory proportional to the declared structure rather than the actual payload size. For example, a 1 MB payload that declares a deeply nested structure could cause tens of gigabytes of allocation. The Node.js process exhausts its available heap and triggers FATAL ERROR: Reached heap limit Allocation failed, terminating the process.

Step 4 — Post-Exploitation Impact: The immediate impact is a crash of the server process. In a typical single-node deployment, the site becomes unavailable until restarted. In containerized or auto-scaling environments, the orchestrator may restart the container, but the attacker can repeat the request in a loop (low volume is sufficient — a few requests per second) to keep the service in a crash-restart cycle, effectively achieving sustained DoS. Because the vulnerability requires no authentication and has low attack complexity, a single attacker can take down the service from anywhere on the network. There is no post-exploitation lateral movement or data access — the attack is purely availability-focused.

Impact Assessment

CVSS Breakdown (derived from vector): Base score 7.5. Attack Vector: Network (AV:N) — exploitable remotely. Attack Complexity: Low (AC:L) — no special conditions or race windows required. Privileges Required: None (PR:N) — no authentication needed. User Interaction: None (UI:N) — no victim action required. Confidentiality Impact: None (C:N). Integrity Impact: None (I:N). Availability Impact: High (A:H) — complete loss of service availability.

Business Impact: For enterprises running SvelteKit-based customer-facing applications, this vulnerability enables a trivial remote DoS. A competitor, hacktivist, or financially motivated attacker can disrupt revenue-generating services, e-commerce checkout flows, or critical APIs without any prior access. For internal tools (admin dashboards, internal portals), the impact is operational degradation. Because the CVSS score is 7.5 (High), this warrants immediate attention in vulnerability management programs, particularly for internet-facing deployments.

Affected Systems: All SvelteKit applications using @sveltejs/kit versions 2.49.0 through 2.52.1 that have set experimental.remoteFunctions to true in their Svelte config. Applications on earlier versions or patched versions (>=2.52.2) are unaffected. Applications using remote functions must also have form handling enabled (the default), meaning both configuration flags are conditions for exposure.

Blast Radius: The blast radius is limited to the affected server process. There is no risk of data exfiltration, privilege escalation, or lateral movement. The primary blast radius is time-to-recover (TTR): if the service is not under process supervision, TTR equals manual restart time; if supervised, the attacker can maintain DoS indefinitely with repeated requests. Secondary blast radius includes monitoring noise, potential cascading failures if the crashed process was serving other endpoints, and reputational damage from service unavailability.

Exploitability in the Wild: No evidence of active exploitation or public PoC exists as of this report. The vulnerability is 30 days old at assessment time, and the SvelteKit team historically discloses vulnerabilities without exploit details. The attack requires a non-default configuration, which reduces the immediate attractor for attackers.

Detection Guidance

Sigma Rule

Detects abnormal form POST request patterns to SvelteKit servers attempting remote function deserialization memory exhaustion.

title: SvelteKit Remote Function Memory Exhaustion Attempt
id: 2c7d1c4e-9f3a-4e2b-8a6d-3f1b0c9e5d7a
status: experimental
description: Detects crafted form POSTs targeting SvelteKit remote function deserialization that may trigger CVE-2026-82260 memory exhaustion.
author: valtersit.com Threat Intel
date: 2026/02/15
logsource:
  category: webserver
  product: nginx
  service: http
detection:
  selection_personalized:
    cs-method: 'POST'
    cs-uri-extension:
      - 'form'
      - 'remote'
    sc-content-type:
      - 'application/x-www-form-urlencoded'
      - 'multipart/form-data'
    cs-user-agent|contains|all: # Suspicious UA patterns sometimes seen in DoS tools
      - 'curl'
  selection_fuzz:
    cs-bytes|gte: 52428800  # 50MB+ body size
  selection_nested:
    cs-uri-query|contains|all:
      - '%5B%5B%5B'  # [[[ encoded nested brackets
  condition: selection_personalized and (selection_fuzz or selection_nested)
  timeframe: 5m
level: high
falsepositives:
  - Legitimate file uploads exceeding 50MB
  - API clients sending legitimate nested JSON structures via form
fields:
  - clientip
  - cs-method
  - cs-uri-stem
  - cs-bytes

YARA Rule

Detects text patterns in web server logs or captured traffic that indicate repeated nested bracket structures or excessively long field keys targeting SvelteKit forms.

rule SvelteKit_RemoteFunction_MemoryExhaustion_Logs
{
    meta:
        author = "valtersit.com Threat Intel"
        description = "Detects log entries indicating malformed form data targeting SvelteKit remote functions (CVE-2026-82260)"
        version = "1.0"
        date = "2026-02-15"
        cve = "CVE-2026-82260"

    strings:
        $nested = /(\[\s*\[\s*\[\s*\[\s*\[\s*\[\s*\[\s*\[\s*\[)/  // 9+ nested brackets
        $longkey = /([A-Za-z0-9_\-]{256,})=/  // field name > 256 chars
        $multicontent = /Content-Length:\s*\d{9,}/  // Content-Length > 1GB
        $sveltekit = /sveltekit/i
        $remoteFunc = /remoteFunction|remote_function|remoteFunctions|remote_functions/i

    condition:
        uint16(0) == 0x0A0D and  // file is a text log (newline at start)
        any of ($longkey, $multicontent) and
        (any of ($nested) or all of ($sveltekit, $remoteFunc))
}

Suricata IDS Rule

Detects anomalous form POST traffic to SvelteKit endpoints with excessive nested bracket structures or oversized bodies.

alert http any any -> any any (msg:"ET WEB_SERVER SvelteKit Remote Function Memory Exhaustion Attempt (CVE-2026-82260)"; flow:established,to_server; http.method; content:"POST"; http.content_type; content:"application/x-www-form-urlencoded"; http.content_type; content:"multipart/form-data"; http.uri; content:"form"; http.request_body; content:"[[[["; depth:32; http.request_body; content:"[[[["; within:0; distance:0; http.request_body; content:"[[[["; within:0; distance:1; http.request_body; content:"[[[["; within:0; distance:1; http.request_body; content:"[[[["; within:0; distance:1; http.request_body; content:"[[[["; within:0; distance:1; http.request_body; content:"[[[["; within:0; distance:1; http.request_body; content:"[[[["; within:0; distance:1; http.request_body; content:"[[[["; within:0; distance:1; http.request_body; content:"[[[["; within:0; distance:1; http.request_body; content:"[[[["; within:0; distance:1; http.content_len; >=:52428800; sid:2026822601; rev:1; metadata:created_at 2026_02_15, updated_at 2026_02_15; classtype:denial-of-service; reference:cve,2026-82260;)

Elastic Detection

EQL query monitoring web server logs for oversized form submissions or repeated nested bracket patterns in URIs.

sequence by host.name with maxspan=5m
  [ network where network.protocol == "http" and http.request.method == "POST" and (
      http.request.body.bytes >= 52428800 or
      http.request.uri like "*form*"
    )
  ]
  [ file where event.category == "file" and process.name == "node" and
      file.extension == "log" and file.path like "*nginx*"
  ]
  | head 50
| where http.request.body.bytes >= 52428800 or
        http.request.uri like "*[[[[" or
        http.request.headers.content_type in ("application/x-www-form-urlencoded", "multipart/form-data")

Splunk SPL Query

Search access logs for form POSTs with excessive body sizes or nested bracket patterns targeting SvelteKit applications.

index=web sourcetype=access_combined
| where method="POST"
| eval uri_has_nested = if(match(uri, "\[\[\[\["), 1, 0)
| eval body_too_large = if(bytes > 50000000, 1, 0)
| where uri_has_nested=1 OR body_too_large=1
| eval suspicious = if(uri_has_nested=1 AND body_too_large=1, "CRITICAL", "SUSPICIOUS")
| table _time, clientip, uri, bytes, suspicious
| sort - _time
| stats count by clientip, suspicious
| where suspicious="CRITICAL"

Wazuh OSSEC Rule

Wazuh rule for monitoring SvelteKit server logs for fatal error messages indicating heap exhaustion from malformed form data.

<rule id="100822" level="12">
  <decoded>
    <program_name>node</program_name>
  </decoded>
  <match>FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory</match>
  <regex>@sveltejs/kit|sveltekit</regex>
  <description>SvelteKit server process crashed due to heap exhaustion — potential CVE-2026-82260 (remote function memory DoS).</description>
  <group>denial_of_service,memory_exhaustion,</group>
  <mitre>
    <id>T1498.001</id>
  </mitre>
  <options>no_full_log</options>
  <frequency>2</frequency>
  <timeframe>60</timeframe>
</rule>

<rule id="100823" level="9">
  <decoded>
    <program_name>node</program_name>
  </decoded>
  <match>allocation failure</match>
  <regex>sveltekit|remoteFunction|remote function</regex>
  <description>Memory allocation failure in SvelteKit remote function context — possible DoS probing (CVE-2026-82260).</description>
  <group>denial_of_service,</group>
  <mitre>
    <id>T1498.001</id>
  </mitre>
  <options>no_full_log</options>
</rule>

Mitigation & Patch Guidance

Current Patch Status: Patch confidence is 0/4 (UNPATCHED) from independent tracking sources. The NVD description confirms a fix exists in version 2.52.2, but no vendor advisory, changelog entry, or GitHub commit has been independently verified by our tracking systems. This discrepancy suggests the fix may be recent or silently released; users should prioritize verifying the version upgrade immediately.

1. Immediate Mitigations (apply now):

• If experimental.remoteFunctions is enabled, disable it immediately in svelte.config.js by setting experimental: { remoteFunctions: false }. This removes the vulnerable code path entirely, as the deserializer is only invoked when this feature is active.
• If the feature cannot be disabled (business-critical remote function usage), place a reverse proxy (Nginx, HAProxy) in front of the SvelteKit server and enforce a strict request body size limit. Set client_max_body_size 5m; in Nginx or equivalent. This mitigates the attack class by rejecting oversized payloads before they reach the Node.js process.
• Add rate limiting on form endpoints to limit the frequency of POST requests per source IP (e.g., Nginx limit_req_zone with 10 req/s burst of 20).

2. Patch / Upgrade Steps:

• Upgrade @sveltejs/kit to version 2.52.2 or later in your project: run npm update @sveltejs/kit and verify with npm ls @sveltejs/kit.
• After upgrading, re-run your integration tests focusing on remote function behavior, as the patch may alter deserialization semantics.
• Check if the SvelteKit project has published a security advisory (monitor the GitHub repository sveltejs/kit releases page and the npm package page for a security notice).

3. Long-Term Hardening:

• Pin SvelteKit versions in package-lock.json and integrate automated dependency scanning (e.g., Snyk, Dependabot, Renovate) to catch future disclosed vulnerabilities within 24 hours of CVE publication.
• Review all applications for experimental features that may not be consistently covered by automated scanning tools — experimental modules are often excluded from default CVE scanners.
• Implement process supervision (systemd, PM2, Kubernetes liveness probes) with auto-restart to minimize downtime from any future DoS.
• For internet-facing deployments, place the Node.js server behind a CDN or WAF that can filter request-byte-size anomalies before reaching the origin.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-82260 — Official NVD record providing the description, CVSS vector, and version range.
2. SvelteKit GitHub Releases: https://github.com/sveltejs/kit/releases — Monitor for the official advisory and release notes for 2.52.2; as of this report, no security advisory has been linked from the CVE.
3. SvelteKit npm Package Page: https://www.npmjs.com/package/@sveltejs/kit — Check the version history and deprecation notices; the 2.52.2 release should be visible here.
4. CWE-400 Reference: https://cwe.mitre.org/data/definitions/400.html — Uncontrolled Resource Consumption, the vulnerability class taxonomy reference.
5. CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog — No entry for CVE-2026-82260 as of this report (KEV status: NO); monitor for future inclusion if exploitation is observed.

Threat Actor Campaigns / Exploit-in-the-Wild: As of the publication date of this report, there is no evidence of active exploitation, no public exploit code, and no threat actor campaigns attributing to this CVE. The vulnerability is considered high-risk due to its trivial exploitation complexity, but the non-default configuration requirement limits broad automated scanning. Organizations should treat this as a high-priority patch item, as public PoC release is likely once the wider community analyzes the fix diff in version 2.52.2.